How to Reduce Mycotoxin-induced Vaccination Failure

Ngày tháng: 2017-06-13

Immunotoxic substances such as mycotoxins are unsuspected players in the failure of vaccines to provoke a proper immune response.

Vaccines are commonly used to prevent various pathogenic challenges of viral, bacterial, and protozoan origins that usually lead to diseases affecting health and performance of livestock. Some of the disease challenges in swine where vaccines play a crucial role in preventing and controlling are listed in Table 1.

Table 1. Swine diseases commonly addressed through vaccination.

3 types of vaccines

There are two major types of vaccines normally used in swine production –live and inactivated—while other types of vaccines are seldom used.

1. Live, attenuated vaccines

Live-type vaccines contain either virus or bacteria in small amounts with the objective to infect the host and multiply in its body to produce immunity, preferably with minimal reaction. This leads to the recognition of increased amounts of the same type of pathogen by the host’s immune system, thus resulting in an enhanced immune response.

2. Inactivated/killed vaccines

Inactivated/killed vaccines have inactivated and processed virus or bacteria which then stimulates the immune system for a longer period of time inside the host. Inactivated vaccines are usually combined with an adjuvant (an oil or aluminum hydroxide) to increase their stability, and to stimulate the host immune response.

3. Other

These include toxoids (contain inactivated toxin of a bacterial pathogen), subunits/conjugates (contain pieces of the pathogen they protect against), and recombinant (contain virus with gene code for a vaccine protein against another virus) vaccines. Autogenous vaccines (autovaccines) are for therapeutic use, individually tailored for a host, made from cultures of pathogens isolated from the infection site.

The immune response

Two different mechanisms are involved in establishing an immune response: the inflammatory and acquired immune responses.

1. The inflammatory response

Inflammation is a non-specific response that occurs very rapidly and leads to the activation of phagocytes (macrophages and neutrophils). The activated phagocytes secrete many different molecules such as cytokines (involved in the recruitment and the activation of other cells)

2. The aquired immune response

Acquired immune responses are associated with immunogenic memory carried out by B cells (humoral) and memory T cells (cellular). These cells are generated from naïve precursor cells after exposure to the microbial antigens. Upon interaction with the antigen presenting cells, B cells start to secrete specific antibodies. Naïve T cells rapidly proliferate and differentiate into effector T cells which target the host cells infected by pathogens. This phase of proliferation is followed by a contraction phase during which about 90% of the effector T cells die, whereas the remaining cells differentiate into memory T cells. Thus the immune response is highly complex and various cells interact with one another to produce the desired effect.

Causes and consequences of vaccination failure

Factors leading to higher rates of vaccination failure result either from 1) a failure to provide potent vaccines properly to the host or 2) immune suppression in the host.

Vaccine delivery can be hampered by contamination, improper storage or procedural errors. The five factors causing immune suppression directly in the animal include stress, poor nutrition, infectious agents, maternal antibody interference, and mycotoxins.

These major causes and corrective measures are listed in Table 2. The good news is that these factors can largely be overcome by employing good management practices, including proper vaccine storage, handling and training.

Stress (physical or psychological)

Weaning, crowding, mixing, shipping, restraint, limit-feeding, noise, and excess heat or cold are some of the common stressors proven to affect the immune response.

Improper nutrition

Overfeeding or malnutrition can lead to impaired immune response as the nutritional cost of the activation and maintenance of acute immune response has been about 10% of dietary protein and 1.1 g/kg of metabolic body weight (BW) in pigs.

Infectious agents

Certain infectious agents can predispose the animal to secondary bacterial infection by suppressing specific immune function. For example, PRRSv can increase the susceptibility to pneumonia in pigs.

Maternal antibody interference

Piglets without maternal antibodies can be vaccinated as early as one day of age. However in herds where vaccination is routinely done, piglets will have circulating maternal antibodies that could block the immune response against the vaccine.

Researchers have found that 60% of pigs vaccinated at 3 weeks of age were found seropositive 3 months later; 5 weeks of age had 62%; 6 weeks of age had 79%; 7 weeks of age had 96%; 8 weeks of age had 100%, and at 9 weeks of age had 87%.

Aflatoxin B1 has been reported as a cause of immunization failure with Erysipelothrix rhusiopathiae bacterins, as well as increased the severity of coccidiosis infection.

Ochratoxin A increased the susceptibility of pigs to natural infection by Salmonella cholerasuis, Serpulina hyodysenteriae or Campylobacter coli.

T-2 toxin has been found to increase the susceptibility to Salmonella, Listeria monocytogenes, Staphylococcus aureus, and Cryptosporidium baileyi.

Deoxynivalenol (750 ppb) has been shown to increase Salmonella invasion 10 times in porcine epithelial cells, and is highly toxic to lymphocytes.

Fumonisin (500 ppb) has been found to increase the intestinal colonization of hemolytic Escherichia coli in piglets. Fumonisin has also been found to inhibit cell proliferation and alter cytokine production.

The combination of deoxynivalenol and fumonisins, even at sub-clinical doses, can impair liver and intestinal integrity resulting in impaired vaccine response (Figures 3 and 4).

Summary

Overall, proper vaccination programs along with good management practices can help overcome most of the factors that cause vaccination failure.

However, specific immunotoxic substances such as mycotoxins, while often overlooked can inflict real harm and lead to higher treatment costs. Consequently, an effective and comprehensive mycotoxin risk management program is advised.

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